Description: (Applicant's abstract) The energetics governing the folding and function of membrane proteins is less well understood than for water-soluble ones. Thus, while there are abundant data concerning the free energy associated with the burial of an apolar group or the formation of a hydrogen bond in water-soluble proteins, such data are virtually non-existent for membrane proteins. We will determine how amino acid substitutions in the membrane protein bacteriorhodopsin affect its free energy of stabilization. It has been hypothesized that although water-soluble and membrane proteins differ greatly in the polarity of water-facing versus membrane lipid-facing residues, their interior side-chain packing and residue polarities are highly similar. To test this guiding hypothesis we will convert water-soluble proteins into membrane-soluble proteins and vice versa. Our specific aims, then, are: - Aim 1. Membrane-soluble versions of the water-soluble coiled-coil peptide, GCN4-P1, will be designed, synthesized and characterized in micelles and bilayers. - Aim 2. We will determine the effect of amino acid substitutions on the thermodynamic stability of bacteriorhodopsin. - Aim 3. We will design and characterize a water-soluble version of phospholamban, a 57-residue membrane protein that forms transmembrane pentamers. In each case, the thermodynamic properties of the proteins will be thoroughly examined to provide a deeper, quantitative understanding of membrane protein structure.